The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.
Dramatic developments of computer, electronics and communication technologies in recent times have realized various network communication services to offer. This has led to developments of wired communication and wireless communication services beyond the voice service towards ongoing multimedia communication services for transmitting data such as packet data.
The data demand has been increasing continuously, and the explosive growth of smart phones makes it predictable that traffic demands will grow ever more by time. Trying to resolve the increasing traffic, a cloud based network technology has been developed wherein a network is divided into an upper parent group and sub-groups, of which the parent group is centralized and the sub-groups are distributed to service the local areas in need, and thereby provides an efficient resource management, which is called C-RAN (Centralized Radio Access Network).
Existing passive networks have their advantages of allowing an easy installation of a base station to where it is necessary to add, but the integrated management of base stations is difficult, providing no line protection, resulting in deteriorated operational reliability. In addition, a conventional base station needs to colocate a digital signal processing apparatus (corresponding to a base band unit or BBU detailed hereinafter) and a wireless signal transmitting/receiving unit (corresponding to a remote radio head or RRH detailed hereinafter), of which the former generates high heat which requires added facilities such as an air conditioner. Then, such added base stations mean increased wastes of spaces and an increased cost of installations. The C-RAN is the proposed structure in order to solve these deficiencies.
In the C-RAN, with a terminal as a reference point, a network at the prior stage to the terminal is called a fronthaul, and another network at its rear stage is called a backhaul, of which the fronthaul structure mainly characterizes the C-RAN. The digital signal processing apparatus (BBU) has a high unit price, occupies a lot of space for amenities such as air conditioning, and requires ongoing management due to a profuse heat generation. To the contrary, the radio signal transmitting and receiving apparatus (RRH) has a low unit price, occupies less space, and generates less heat, making it easy to manage. Thus, the fundamental concept of the backhaul is to centralize a digital signal processing apparatus (BBU) and to distribute radio signal transmitting and receiving apparatuses (RRH).
In the fronthaul, the digital signal processing apparatus (BBU) and the radio signal transmitting and receiving apparatuses (RRH) are interlinked via an optical network. The physical topologies selected in an optical network design include a ring shape, a bus shape and a star shape among others. Of these, the ring topology allows an easy restoration work at the time of system switchover due to natural disasters or accidents, and it has been recognized for its reliability in backbone network for a long time. Therefore, the connection of the optical fiber cable in the fronthaul is generally established in the form of ring topology which needs less consumption of fiber optic cable and provides a protective switchover function.
However, if a switchover occurred in the fronthaul which is configured in a ring topology changes the signal transmission direction to possibly change the network latency, there is a risk of an error generated thereby from various control operations performed based on latency.
As an example, one of different methods in which a terminal performs a handover is to utilize latency. Upon receiving radio signals from a plurality of base stations, the terminal may measure the latencies of the respective radio signals to determine the base station with the shortest latency and perform the connection with that base station. In other words, if the shortest latency status transitions from base station A to base station B due to a movement of the terminal, the terminal performs a handover to base station B.
When a switchover occurred in the fronthaul in the ring topology changes the signal transmission direction to change the network latency despite no movement of the terminal, a handover may be carried out thereby to any other base station even if no handover is actually necessary.